Adaptation of trees to the urban environment : Acacia karroo in Potchefstroom, South Africa / by Alida Yonanda Pelser

Abstract:

Urban open spaces are of strategic importance to the quality of life of our increasingly
urbanized society. Trees and related vegetation are planted and managed within the
communities and cities to create or add value to the busy lives of the city dwellers.
Trees in towns and cities form an important part of complex urban ecosystems and
provide significant ecosystem services and benefits for urban dwellers, for example:
reducing particulate pollution, carbon sequestration, decreasing air temperature,
decreasing water runoff, aesthetic value and an increase in human health. Trees are solarpowered
technology that can help restore balance to dysfunctional urban ecosystems.
Trees form strands in the urban fabric that connect people to nature and to each other.
The urban environment puts tremendous strain on trees by trenching, limited space for
root growth and emission of pollutants into the atmosphere, water and soil. The problem
is that the real impact of the urban environment on the trees within our community is
unknown.
The aim of this investigation was to assess the overall anthropogenic and environmental
impacts on urban trees by measuring the tree vitality of Acacia karroo using chlorophyll
fluorescence kinetics (JIP-test) and the leaf water potential using a pressure chamber.
Tree vitality was quantified as the chlorophyll fluorescence-based performance index
(PIABS)T. ree vitality measurements were also correlated with soil physical and chemical
data. In the comparative study, an urbanization gradient approach was followed in which
results of trees in rural areas were regarded as controls. The gradient approach is used
worldwide and provides a background for questions of ecological structure and function.
The urbanization gradient was quantified using the V-I-S model, based on % cover of
vegetation, impervious surface and soil. Additionally, a model to determine the monetary
value of trees in urban environments (SATAM) was tested. All this information could
eventually contribute to develop an urban tree management program for Potchefstroom. It was evident from the current study that urbanization has a negative impact on tree
vitality. The leaf water potential of a tree was, however, not necessarily negatively
impacted upon. Although trees in urban environments did not always have a high vitality
(PIABS)t, hey still played a major role in the urban environment. According to the tree
appraisal method (SATAM), some of these trees have a value of R60 000.